I probably shouldn't be surprised to hear that because my experiences are similar and I understand that this is the case for most people.

My advice would be to work on projects that you are intrinsically motivated to work on. Don't work on a project in expectation of any reward if you complete it. Let yourself know that it's ok if you don't achieve all (or any) of what you might have set out to achieve in the first place. Myself, the side projects where I've achieved the most have been ones that give me a dopamine hit (basically games or things that are graphical, in my case, even though I've rarely been paid to work on those sorts of things in my career as a software engineer).

If you're interested in reading up on motivation then there are few books that I've found really useful:

- Drive by Daniel Pink talks about the different types of motivation (intrinsic vs extrinsic) and talks about the motivating factors of autonomy, mastery and purpose. There's a nice sketchnote video based on a talk by the author that did the rounds a few years ago https://www.youtube.com/watch?v=KgGhSOAtAyQ that sums up the key points.

- The Power of Habit by Charles Duhigg talks about habits, how they form and how you can understand and hack them.

- The Power Of Full Engagement by Jim Loehr and Tony Schwartz talks about managing different aspects of your life in order to have energy to do the things that are important to you.

Hopefully the above may be of some use to you. They have been very useful for me, particularly in understanding how counterintuitive human psychology is in some cases and in terms of understanding how some strategies that you may be tempted to use can be counterproductive.